fix(README): remove section on holders directory
fix(README): remove section on holders directory

This isn't implemented yet. Delete it.

marineam/locksmith,crawford/locksmith,coreos/locksmith,marineam/locksmith,npateriya/locksmith,jonboulle/locksmith,coreos/locksmith,npateriya/locksmith,crawford/locksmith,mischief/locksmith,chrissnell/locksmith,jonboulle/locksmith,mischief/locksmith,chrissnell/locksmith